The invention relates to a mechanical valve prosthesis that includes a base having an external portion forming a suture ring, and an internal portion forming a rim, in which a blood flow can move in a main flow direction (F), as well as at least two closing leaflets (10) which can move, under the action of the blood flow, between a closed position and an open position, and vice versa. The opening occurs in the physiological direction, that is from the axis of the rim (3) of the center of the prosthesis and thus toward the rim. A region (40) of each one of the leaflets (10) borders, in the open position, a natural wall and defines with it the peripheral duct regions (19). The region (40) of each leaflet (10) presents a zone (22) in which, in the closed position, it turns its concavity toward the rim (3). In this manner, when the leaflet (10) is in the open position, the peripheral duct regions (19) present a form which produces a beginning of closing of the valve (10) during the deceleration of the blood flow.